page_title: Theatrical smoke and fog
section_title: Fog
hierarchical_section_title: Theatrical smoke and fog / Types of effects / Fog
context_page_description: Theatrical smoke and fog, also known as special effect smoke, fog or haze, is a category of atmospheric effects used in the entertainment industry. The use of fogs can be found throughout motion picture and television productions, live theatre, concerts, at nightclubs and raves, amusement and theme parks and even in video arcades and similar venues. These atmospheric effects are used for creating special effects, to make lighting and lighting effects visible, and to create a specific sense of mood or atmosphere. If beams of light are visible cutting across a room, that most likely means smoke or fog is being used. Theatrical smoke and fog are indispensable in creating visible mid-air laser effects to entertain audiences. Recently smaller, cheaper fog machines have become available to the general public, and fog effects are becoming more common in residential applications, from small house parties to Halloween and Christmas.
  Theatrical fog and theatrical fog machines are also becoming more prevalent in industrial applications outside of the entertainment industry, due to their ease of use, inherent portability and ruggedness.
context_section_description: Fog is created by pumping one of a variety of different glycol or glycol/water mixtures (referred to as fog fluid) into a heat exchanger (essentially a block of metal with a resistance heating element in it) and heating until the fluid vapourises, creating a thick translucent or opaque cloud.  Devices specifically manufactured for this purpose are referred to as fog machines.
  An obsolete method for creating theatrical fog on-stage (although the technique is still commonly used in motion pictures) is to use a device known as a thermal fogger, initially designed for distributing pesticide, which aspirates a petroleum product (typically kerosene or propane), ignites the fuel, and then mixes in air and pesticide to create a dense fog.  For theatrical purposes the pesticide is typically replaced with glycol, glycol/water mixtures, or water.  This technique is similar to the smoke generators used by military forces to create smoke screens, and is generally only used outdoors due to the volume of fog produced and the petroleum fuel required.
  "Low-lying" fog effects can be created by combining a fog machine with another device designed specifically for this purpose.  As the fog exits the fog machine it is chilled, either by passing through a device containing a fan and ice, or by passing through a device containing a fan and compressor similar to an air conditioner.  The result is a relatively thick fog that stays within a few feet of the ground.  As the fog warms, or is agitated, it rises and dissipates. Several manufacturers of theatrical fog fluid have developed specially formulated mixtures specifically designed to be used with CO
  2, intended to provide thicker, more consistent fog effects.  Although these chilling devices do not use carbon dioxide, the specially formulated fog fluid does create denser fog than regular fog fluid.
caption: A thermal fogger and fan on a movie set
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